1. Field of the Invention
The present invention relates to a composition and a polymer molding composition used for forming a fluorescent molded product such as a wavelength conversion layer which emits fluorescence by irradiation with excitation light, and a wavelength converter obtained using the same. The present invention also relates to a wavelength conversion member having a wavelength conversion layer, a backlight unit including the same, and a liquid crystal display device.
2. Description of the Related Art
A flat panel display such as a liquid crystal display device (LCD) has been more widely used as a space-saving image display device having low power consumption. A liquid crystal display device includes at least a backlight and a liquid crystal cell and typically further includes a member such as a backlight-side polarizing plate or a visible-side polarizing plate.
Recently, a configuration in which a wavelength conversion layer including quantum dots (QDs) as a light emitting material is provided in a wavelength conversion member of a backlight unit in order to improve color reproducibility of an LCD has attracted attention (refer to US2012/0113672A). The wavelength conversion member converts the wavelength of light incident from a light source so as to emit white light. In the wavelength conversion layer including the quantum dots as a light emitting material, white light can be realized using fluorescence which is emitted by excitation of two or three kinds of quantum dots having different light emitting properties caused by light incident from a light source.
The fluorescence emitted from the quantum dots has high brightness and has a small half-value width. Therefore, an LCD using quantum dots has excellent color reproducibility. Due to the progress of such a three-wavelength light source technique using quantum dots, the color reproduction range of an LCD has been widened from 72% to 100% in terms of National Television System Committee (NTSC) ratio.
It is known that permeation of oxygen is necessarily suppressed in a layer including quantum dots (hereinafter, referred to as “QD layer”). In a case where oxygen permeates into a QD layer, there is a problem in that the emission intensity decreases due to photooxidation caused by contact between quantum dots and oxygen.
In order to solve the problem, a configuration of a wavelength conversion member is disclosed in which a barrier film which suppresses permeation of oxygen is provided outside of a QD layer in order to protect the quantum dots from oxygen permeated from the outside of the wavelength conversion member (for example, US2012/0113672A).
Typically, for example, the following configurations of a barrier film are known: a configuration in which substrates having oxygen barrier properties are used as supports between which a QD layer is interposed such that the substrates themselves are used as barrier films; and a configuration in which an inorganic harrier layer or an organic barrier layer having oxygen barrier properties is provided on a surface of a support. As the inorganic barrier layer having oxygen barrier properties, an inorganic layer formed of an inorganic oxide, an inorganic nitride, an inorganic oxynitride, a metal, or the like is preferably used.
However, the configuration of the wavelength conversion member in which a barrier film is provided outside of the QD layer as described in US2012/0113672A can suppress the permeation of oxygen into the QD layer to some extent. For example, in a case where a wavelength conversion member having a long film shape is formed and then cut to manufacture a wavelength conversion member having a desired size, a QD layer is exposed to external air from a cut side surface. Therefore, a countermeasure against permeation of oxygen from the cut side surface is also required.
WO2011/031876A and WO2013/078252A disclose a configuration in which a QD layer includes a light stabilizer. WO2011/031876A and WO2013/078252A describe that, since the light stabilizer is present in the layer, effects of oxygen permeated into a barrier film, effects of oxygen permeated from a side surface, and the like can be reduced. In addition, US2013/0313595 discloses a quantum dot-containing bead containing a reducing agent such as ascorbic acid, palmitic acid, or alpha tocopherol (vitamin E).